1. Field of the Invention
The present invention relates to a method for measuring the roughness of the surface of a material and more particularly to a method of measuring the roughness of a material surface by measuring a light scattering ellipse reflected off the surface along the scattering ellipse's minor axis.
2. Discussion of the Related Art
Such a method is known from Swiss patent 552 197. Moreover, it is proposed to use a line of detectors along the major axis of the scattering light ellipse which arises in the event where the surface of the material shows a certain roughness and is illuminated by a bundle of parallel light beams under a predetermined angle. Preferably there the scattering light cone at the half width in the vicinity of the glancing angle is measured and is used as a measure for the roughness of the investigated surface. Furthermore, an evaluation using a television camera instead of an evaluation with a line of detectors is described.
The evaluation of the roughness is of remarkable importance at the manufacturing of paper since the roughness or reciprocally the smoothness gives evidence about the printability of the paper.
In the known device it must be cared for that at the location of the illumination of the web of material by the bundle of light beams this web has to be guided in such a way that due to the movement no too large positional changes result in the plane where the web of material extends in order to avoid that the scattering light ellipse is moving out of the scanning area of the detector. The same problem results where the surface to be measured is too rough so that the scattering light distribution within the major axis of the scattering light ellipse is exceeding the scanning field as provided by the line of detectors or the television camera, respectively.